Unable to sleep at night? Try writing a "to-do" list at bedtime as it may aid in falling asleep, a new study suggests.

"Most people just cycle through their to-do lists in their heads, and so we wanted to explore whether the act of writing them down could counteract night time difficulties with falling asleep," said lead author of the study Michael K. Scullin from Baylor University, in the US.

The study compared sleep patterns of participants who took five minutes to write down upcoming duties versus participants who chronicled completed activities.

"There are two schools of thought about this. One is that writing about the future would lead to increased worry about unfinished tasks and delay sleep, while journaling about completed activities should not trigger worry," Scullin said.

"The alternative hypothesis is that writing a to-do list will 'off-load' those thoughts and reduce worry," he added.

For the study, published in Journal of Experimental Psychology, researchers monitored electrical brain activity using electrodes on a group of healthy young adults.

They completed a writing assignment for five minutes prior to overnight polysomnography recording in a controlled sleep laboratory.

They were randomly assigned to write about tasks that they needed to remember to complete the next few days (to-do list) or about tasks they had completed the previous few days (completed list).

Participants in the to-do list condition fell asleep significantly faster than those in the completed-list condition.

The more specifically participants wrote their to-do list, the faster they subsequently fell asleep, whereas the opposite trend was observed when participants wrote about completed activities.

Therefore, to facilitate falling asleep, individuals may derive benefit from writing a very specific to-do list for five minutes at bedtime rather than journaling about completed activities, the researchers noted.